PLEASE HELP!!!

[Taekdown918]

I am out of ideas. I have been working on my daughters 1999 GMC Sierra 5.3L with 148K miles on it for 5 months. It has a P0342 code that will not go away. The truck runs great so I have not been in a hurry but she now has emissions next month so I have to get it fixed. Here are the things I have done so far.

 

1. Replaced the CanShaft Position Sensor twice with OEM

2. Replaced the CrankShaft Position Sensor praying it might help.

3. Replaced the wiring connector to the sensor with a new one.

4. Put a new ECM in today including the pain in the butt security learn.

5. Toned the lines back to the ECM to make sure they are not broken somewhere.

6. Checked every ground I could find.

 

All of this including the new ECM and it still throws the P0342 Low Voltage code. I can reset it and while it is running it will pop as pending so I do not think it is the starter. I am going to pull the sensor and look down the hole with my borescope to see if the metal is messed up. The old one had no marks or damage on it at all. What could it be? I have never had this much of an issue tracking down a problem. The truck runs great overall. I am stumped. I read about a jumper but I could not locate it on this truck. It was a friends truck and we got it for my daughter to be able to transport her mother to doctors appointments with her scooter. The code came up a couple days before we bought it along with some codes that needed a tune up overall. I did the full tune up and all the codes went away but this one. Everything runs and there is no other codes coming up other than this one and I have to fix it to get it through emissions since they will not test a vehicle with a code.

 

Thank you in advance. I will take any advice. I even spoke to a local Check Mechanic and he said I did everything he would of done. I was praying the ECM would fix it.

[Taekdown918]

Bump, anyone? Please, ideas.

[Taekdown918]

Bump, Anyone. All of you GMC Experts. Please weigh in.

[silveradosid]

just read on another forum that low fuel pressure can also cause this code. if you got a gauge check to see how long it takes to build up fuel pressure and how much pressure you have

[Buckshot556]

Reset the computer with a code reader right before she goes for her chec

[Taekdown918]

I changed the fuel filter and no help. Resetting is right before would not help since it pops as pending as soon as I reset even while running. Thank you. Ideas please keep coming.

[TexasSilverado16]

Have you tried a new starter & or battery? A faulty starter or bad battery can cause this code to come on. Even bad wiring to the starter.

 

 

TexasSilverado16

[Taekdown918]

I pout a brand new battery in today and a new starter. I checked the wiring to the starter and it is the same as the battery. Dumb question, can I run three new wires from the sensor to right before it goes into the ECM or does it pass through other sensors etc... I also used a scope and looked at the wheel through the hole and it looks great.

[NSFW]

Ring out the block to the firewall. Then check the resistance on the ground from the block to the firewall. It should be 0.00 or damn close. High resistance means the sensor that requires a clear path to ground have a longer then nominal route back to the ECM. Check the ground strappy-doo from the block to the firewall on the right side of the left cyl head and make sure that sucker is hooked up. If there is ANY doubt, then run a clipped-jumper straight from the ECM to the block. Clear Code, try again.

The Sensor itself IN DETAIL uses Pulse Width Modulation to function. Theres no DAC between the signal and the ECM.. just wires as the ECM reads the signal straight up no conversion. (Easier to see reference on a scope, not that kind of scope.,.an oscilliscope) On/off like a thermo probe, or a mercury switch is ANALOG and usually goes thru conversion as the ECM is a digital box which only reads digital signals. I had a problem with an antiloc brake malfunction once on a GMT400 1-tonne, and some novice had wrapped the signal wire around the sway bar, before plugging it in to the harness. Simply didn't understand how a twisted pair works, and how sensitive it is to grounding interference. Good idea, but ignorant to whats going on inside them wires.

If you WANT To run a new set of wires, my suggestion is use a twisted pair with shielding. 16 gauge, 16 or 18 as the sensor doesn"t need allot of amps, just voltage. Put the drain on the ECM, and the other drain (sensor side) ground to the block. This will ensure that the digital signal from the sensor wont be garbled up by RF interference from the trucks electrical system, or the environment. And that the sensor is directly grounded to the ECM.

Good luck.

[Taekdown918]

Thank you so much for getting me moving again. I was out of chances. I will give that a look. I will let you know.

[Taekdown918]

Ok guys. I am still battling this and it is now emossions month and it needs to go through. I thought I fixed it. I ran jumper wires from the sensor directly to the ECM since I could not find where to break was. By doing that I finally got the code to clear for the first time. I was so excited. Then bam it came back as pending. I dug in further and I have it down to this. The low voltage wire reads fine until I put it in gear. I noticed the code would not come up at all until I put it in gear then it immediately pops as pending then pops full P0342. So I disconnected the the harness and the low voltage wire reads fine with the key on but as soon as I turn is in gear (no matter what gear) it goes to 0 voltage. It is 0 voltage even at the ECM. We have 15 days to figure this out. PLEASE HELP ME! So far I have

 

Replaced ECM

Tried 3 Camshaft Sensors

Replaced CrankShaft Sensor

New wires

New plugs

New battery

Checked all grounds

Added second wire from sensor to ecm (that is how I got the code to go away while not in gear)

Also replaced the harness and end.

 

I have easily 200 hours of labor in this thing, on a good note I can change the sensor in ten minutes, no joke. I have had it apart so many times.

[Loco-diablo]

I'm certainly no expert and you seem to your stuff, I've read on here that new battery cables have helped with low voltage issues.

 

 

Sent from my iPhone using Tapatalk

[Taekdown918]

A soon as I put it in gear the the low voltage wire goes to zero. It is a weird ghost issue. I can not think of what would cause it to go from correct signal to no signal.

[repairman54]

Transmission positon sensor could be bad pulling down the reference voltage when you put it in gear.

I'd unplug the trans and other related sensors and see if that signal still drops out.

[Taekdown918]

OK Everyone, I unplugged the lower connector on the park sensor and BAM code was gone and the truck ran even better. So I figured the switch was bad so I purchased a new OEM switch and replaced the entire switch on the transmission. Plugged it back in and soon as I put it in gear the P0342 code came back on. I unplugged it again and BAM no code again. She drove it for three days with it unplugged and no codes popped up with it unplugged. The truck runs great and no issues with it as long as I leave the bottom connector unplugged. It has four wires. 3 are low voltage and one is ground. I have no clue what the connector does since all the safety features work like not starting in gear and the back up lamp works. What does the lower plug do? We are just going to run it through emissions with it unplugged since it shows no codes or pending codes. This try is nuts. Any ideas? Any ideas would help. I understand why it works when I unplug it since it is not grounding out but why wouldn't a new sensor of fixed it overall?